An interaction between locus coeruleus activation modes and heterogeneous adrenoceptor expression in the basolateral amygdala for valence signaling

Abstract

The locus coeruleus (LC) is a neuromodulatory brainstem nucleus which signals arousal via the release of norepinephrine (NE) throughout the central nervous system. Norepinephrine facilitates adaptive behavioural responding, perception, and learning and memory via enhancing the signal-to-noise ratio at downstream structures. The LC has recently been suggested to be involved in positive and negative valence signaling via two distinct activation modes, phasic and tonic. This effect has been shown to depend on adrenoceptor engagement in the basolateral amygdala (BLA). Here, we sought to determine whether phasic and tonic modes of LC activation differentially engage functionally distinct subpopulations of the BLA and whether naturally-produced valence recruits the same circuitry. Finally, we investigated the adrenoceptor profile of these subpopulations, as our valence effects may depend on their unique adrenoceptor expressions. Phasic and tonic LC photostimulation preferentially recruited nucleus accumbens (NAc)- and central amygdala (CeA)-projecting subpopulations of the BLA in the presence of an odor, respectively. Natural reward and aversive learning showed patterns of BLA activation similar to that of phasic and tonic LC photostimulation, respectively. Immunohistochemistry revealed differences in adrenoceptor expression across BLA subpopulations. These findings offer a mechanism underlying the differential valence effects of phasic and tonic LC activation.